An injection device includes a housing, a plunger, a drive gear and a release trigger. The plunger includes a leadscrew and a cap attached thereto where, in use, the cap engages a bung of a cartridge containing medicament. The drive gear within the housing engages with the leadscrew such that rotation of the drive gear around the leadscrew drives the plunger axially through the housing towards the bung. The trigger includes a locking ring having generally axially extending teeth for engaging with corresponding teeth on the drive gear. The trigger is generally axially movable between an engaged position where the teeth are engaged and prevent rotation of the drive gear, and a disengaged position where the teeth are disengaged and enable rotation of the drive gear. Movement of the trigger between the disengaged and engaged position causes counter-rotation of the drive gear and retracts the plunger away from the bung.
